This invention relates to a catalytic cracking catalyst and is particularly concerned with a cracking catalyst having a high attrition resistance, a process for making such a catalyst and a process for using such a catalyst.
Fluidized catalytic cracking (FCC) units are used in the petroleum industry to convert high boiling hydrocarbon feedstocks to more valuable hydrocarbon products, such as gasoline, having a lower average molecular weight and a lower average boiling point than the feedstocks from which they were derived. The conversion is normally accomplished by contacting the hydrocarbon feedstock with a moving bed of catalyst particles in the substantial absence of added hydrogen at temperatures ranging between about 800.degree. F. and about 1100.degree. F. The most typical hydrocarbon feedstock treated in FCC units comprises a heavy gas oil, but on occasion such feedstocks as light gas oils or atmospheric gas oils, naphthas, reduced crudes and even whole crudes are subjected to catalytic cracking to yield low boiling hydrocarbon products.
Catalytic cracking in FCC units is generally accomplished by a cyclic process involving separate zones for catalytic reaction, steam stripping, and catalyst regeneration. The hydrocarbon feedstock is blended with an appropriate amount of catalyst particles to form a mixture that is then passed through a catalytic reactor, normally referred to as a riser, wherein the mixture is subjected to a temperature between about 800.degree. F. and about 1100.degree. F., normally between about 900.degree. F. and 1050.degree. F., in order to convert the feedstock into gaseous, lower boiling hydrocarbons. After these gaseous, lower boiling hydrocarbons are separated from the catalyst in a suitable separator, such as a cyclone separator, the catalyst, now deactivated by coke deposited upon its surfaces, is passed to a stripper. Here the deactivated catalyst is contacted with steam to remove entrained hydrocarbons that are then combined with vapors exiting the cyclone separator to form a mixture that is subsequently passed downstream to other facilities for further treatment. The coke-containing catalyst particles recovered from the stripper are introduced into a regenerator, normally a fluidized bed regenerator, where the catalyst is reactivated by combusting the coke in the presence of an oxygen-containing gas, such as air, at a temperature which normally ranges between about 1000.degree. F. and about 1500.degree. F. The cyclic process is then completed by blending the reactivated catalyst particles with the feedstock entering the riser or reaction zone of the FCC unit.
In the cyclic process described above, the catalyst particles encounter mechanical stresses when they collide with each other within the walls of the FCC unit. These stresses cause the catalyst to attrit into smaller particles which can escape from the FCC unit into the atmosphere. Thus, catalysts which tend to be friable and therefore easily undergo attrition to form smaller particles are highly undesirable. The more fines that are produced by attrition in the unit, the more makeup catalyst that must be added to the unit and the greater the air pollution caused by fines escaping from the unit.
Accordingly, it is one of the objects of the present invention to provide a fluid catalytic cracking catalyst, and method for its preparation, which is highly attrition resistant. This and other objects of the invention will become more apparent in view of the following description of the invention.